The present invention relates to auger type poultry chillers using a counter flow chilled water bath to chill poultry carcasses, and in particular, to the type of poultry chiller in which the chilled water is re-circulated through an external refrigeration unit.
In the processing of poultry for human consumption, it is necessary that the slaughtered, eviscerated poultry carcasses be chilled as rapidly as possible. Various types of poultry chillers to accomplish the chilling of freshly killed poultry are known in the art. Poultry chillers typically employ chilled water to reduce the temperature of the poultry carcasses. For example, U.S. Pat. No. 4,788,831 discloses a drag type chiller in which a series of moving rakes advance the poultry carcasses through a tank of chilling liquid.
Another type of chiller is the auger type as disclosed in U.S. Pat. No. 5,868,000 in which an auger having a series of flights forms a generally helical structure that when rotated moves the poultry carcasses through a chilled water bath. Similar chillers are disclosed in U.S. Pat. Nos. 4,860,554 and 5,484,615.
In some chillers, the chilled water bath is not circulated, i.e., the water either remains in the chiller or is used one time only and discharged. The more common type, however, re-circulates the chilled water. The chilled water may either be circulated through the chiller in the same direction as the movement of the poultry carcasses, as shown in U.S. Pat. No. 4,827,727, or more commonly, in a counter flow in which the chilled water and the poultry carcasses move through the chiller in opposite directions. Such counter flow chillers are disclosed in U.S. Pat. Nos. 4,788,831; 5,868,000; and 4,860,554. Counter flow is known to more efficiently transfer heat from the poultry carcasses to the chilled water.
Two primary means are used to chill the water. One type, exemplified by U.S. Pat. No. 4,860,554, applies cooling to the walls of the chiller, such as by refrigeration coils built into the walls of the chiller or by using a jacket around the walls of the chiller in which a cooling fluid circulates.
In the other type of chiller, the chilled water is sent from the chiller to an external refrigeration source, such as an ammonia refrigeration system, that reduces the temperature of the water that is then re-circulated to the chiller. The external refrigeration may be supplied through a heat exchanger and refrigeration unit such as shown in U.S. Pat. No. 4,788,831. The chilled water enters the chiller at one end, circulates through the chiller, and after being warmed by contact with the poultry carcasses, exits the chiller. The warmed water is again chilled by the refrigeration unit and re-circulated through the chiller.
In auger type chillers, the poultry carcasses tend to sink toward the bottom of the chiller or to clump. In order to obtain maximum efficiency in transferring heat from the poultry carcasses to the chilled water, it is desirable to force the chilled water into intimate contact with the poultry carcasses. This becomes difficult to achieve if the poultry carcasses settle to the bottom of the chiller. Some attempts to solve this problem use air agitators to turbulently tumble the poultry carcasses through the chiller. Other techniques use paddles or other structures to encourage more thorough mixing of the poultry carcasses with the chilled water. It has not been generally recognized, however, that a significant mechanism that reduces the efficiency of heat transfer from the poultry carcasses to the chilled water is inherent in the design of the counter flow auger type chillers which re-circulate the chilled water through an external refrigeration unit.
In this type of prior art counter flow, re-circulating, externally refrigerated auger chiller, the auger rotates in a tank that is generally U-shaped in cross sectional outline, square shaped such as in U.S. Pat. No. 5,484,615, or some other shape that does not conform closely to the outer edges of the auger. U.S. patent application Ser. No. 09/298,364, filed Apr. 23, 1999, which is incorporated herein by reference, discloses a U-shaped tank. U.S. Pat. No. 5,868,000 also appears to show the U-shaped type of tank in which the outline is circular up to approximately the level of the centerline of the auger. From this point upward, the walls of the U-shaped tank are substantially vertical. This arrangement has some mechanical advantages, such as allowing the auger to be easily removed from the tank since the walls of the tank are never narrower than the width of the auger. Another advantage is that the vertical walls lend themselves to the attachment of catwalks for movement of personnel around the chiller for maintenance and other tasks. One disadvantage of this design is that the vertical walls tend to be susceptible to bending and require expensive reinforcement to maintain the necessary structural integrity of the chiller. Another disadvantage is that the shape tends to be inefficiently loaded in that there are limits to how high the water level in the chiller can be and this in turn limits the quantity of poultry carcasses that can be loaded into the chiller at one time. Increasing the loading potential of the chiller requires a larger chiller that cannot be accommodated in the same xe2x80x9cfootprint.xe2x80x9d This can be a significant factor in facilities where space is at a premium.
From the point of view of efficiently cooling the poultry carcasses, the significant disadvantage of the prior art design of counter flow, re-circulating, externally refrigerated auger chillers is that when the walls of the tank do not conform closely to the outer edges of the chiller, two or more triangular shaped gaps are left between the upper walls of the tank and the outer edges of the auger. The chilled water thus tends to take the path of least resistance and to flow between the upper walls of the tank and the outer edge of the auger. By contrast the optimum path of the chilled water through the chiller is a helical path conforming to the flights of the auger. Such a helical path forces a more thorough and intimate contact between the chilled water and the poultry carcasses, even if the carcasses clump toward the bottom of the chiller.
Chillers having walls of semi-cylindrical cross sectional outline are known in the art. For example, U.S. Pat. No. 4,860,554 discloses a counter flow poultry chiller having a semi-cylindrical tank. This chiller is chilled by cooling the walls of the tank directly by refrigeration coils mounted to the exterior walls of the tank. U.S. Pat. No. 4,827,727 also discloses a tank with a semi-cylindrical shape and in which the chilled water is re-circulated to an external heat exchanger. The chilled water and product flow concurrently rather than in a counter-flow arrangement. Chillers manufactured by Barker and Stork Gamco are known in which a semi-cylindrical tank is chilled by liquid circulating through a jacket of double tank walls.
The limitations of the prior art are overcome by the present invention as described below.
The present invention is a counter flow, re-circulating, externally refrigerated auger type chiller. The chiller has a tank that is semi-cylindrical in shape so that the walls of the tank conform closely to the circular cross section of the auger. By minimizing the gap between the walls of the tank and the outer edges of the rotating auger, the counter flowing chilled water is forced to flow in the helical path determined by the auger. This assures a longer residence time for the chilled water in the auger, more thorough and more intimate contact between the poultry carcasses and the chilled water, and thus more efficient transfer of heat from the poultry carcasses to the chilled water.
Such a design also has the added advantages of a more rigid structure that requires less structural reinforcement and more efficient loading of the chiller due to the more efficient geometry of the semi-cylindrical shape of the chiller tank.
Since the design of the present invention forces the chilling water to flow in a helical path along the flights of the auger and denies the more direct path around the auger found in the prior art, the chilling water naturally is subjected to greater head loss in the course of passing through the chiller. As a result the water level at the exit end of the chiller, where the chilling water is introduced, will be higher than at the inlet end of the chiller, where the warmed chilling water leaves the chiller. In an alternative embodiment of the present invention, this effect is alleviated by sloping the chiller downwardly from the exit end to the inlet end.
It is therefore an object of the present invention to provide for a counter flow, re-circulating, externally refrigerated auger type chiller having a semi-cylindrical shape for a more efficient flow path for the chilled water through the poultry carcasses.
It is a further object of the present invention to provide for a counter flow, re-circulating, externally refrigerated auger type chiller with a tank having a semi-cylindrical shape to more efficiently transfer heat from the chilled water to the poultry carcasses.
It is also an object of the present invention to provide for a counter flow, re-circulating, externally refrigerated auger type chiller with a tank having a semi-cylindrical shape to more efficiently load poultry carcasses into the chiller.
It is a still further object of the present invention to provide for a counter flow, re-circulating, externally refrigerated auger type chiller with a tank having a semi-cylindrical shape for greater structural integrity while minimizing the use of reinforcement materials.
These and other objects and advantages of the present invention will be apparent from a consideration of the following detailed description of the preferred embodiments in conjunction with the appended drawings as described following.